1. Field
The present description relates to an ESD transistor and an ESD protection circuit thereof, and to an ESD protection circuit for a high voltage device that can reduce clamping voltage and can shunt high-level ESD current by forming an extended current path in an ESD transistor for high voltage, and an ESD transistor that forms a long current path.
2. Description of Related Art
Electrostatic discharge (hereafter, referred to as “ESD”) technologies are very important for reliability of most integrated circuits or core circuits. Circuit designers can protect a core circuit by implementing an ESD protection circuit with an I/O pad connected to a ground GND, using an ESD transistor connected with the core circuit in parallel.
FIG. 1 is a block diagram illustrating an ESD protection circuit.
Referring to FIG. 1, an ESD protection circuit may be connected to an I/O pad 110 through its drain 105 and to a ground 120 through its source 104, in which a floating-body transistor 101 (or clamp) includes a body 102, a gate 103, the source 104, and the drain 105. The gate 103 is connected to the source 104 and a core circuit 130 is connected to the drain 105 and the source 104 in parallel with the floating-body transistor 101.
However, the ESD protection circuit with the illustrated configuration may exhibit difficulties in shunting high-level ESD currents while maintaining low clamping voltages. For example, in a transistor using high voltage over 20V, the doping concentration in the source 104 and the drain 105 should be low to maintain high break down voltage in the ESD protection circuit. During an event of electric discharge, the ability of the ESD protection circuit to protect the core circuit 130 decreases due to high turn-on voltage induced in the operation of a GGNMOS and a BJT. Even if the ESD protection circuit is turned on, strong snapback is caused by a kirk effect in high current bipolar operation mode. This, in turn, may cause the generation of interface current and a change of BJT turn-on voltage, because damage is frequently generated around a drift doping region and field oxide of an N+ doping boundary.